1. Field of the Invention
The present invention is directed to aluminum titanate ceramic batch mixtures including pore formers, aluminum titanate green bodies including pore formers, and methods for manufacturing and firing aluminum titanate ceramic bodies.
2. Technical Background
Exhaust gases emitted by internal combustion systems utilizing hydrocarbon fuels, such as hydrocarbon gases, gasoline, or diesel fuel, can cause serious pollution of the atmosphere. Among the many pollutants in these exhaust gases are hydrocarbons and oxygen-containing compounds, the latter including nitrogen oxides (NOx) and carbon monoxide (CO). The automotive industry has, for many years, attempted to reduce the quantities of pollutants from automobile engine systems, the first automobiles equipped with catalytic converters having been introduced in the mid 1970's. Cordierite substrates, typically in the form of a honeycomb body, have long been preferred for use as substrates to support catalytically-active components for catalytic converters on automobiles, in part due to cordierite ceramics' high thermal shock resistance. The thermal shock resistance is inversely proportional to the coefficient of thermal expansion. That is, honeycombs with a low thermal expansion have a good thermal shock resistance and can survive the wide temperature fluctuations encountered in their application.
However, in many applications such as, for example, certain diesel particulate filter applications, materials may be required which have a higher level of thermal shock resistance. Thus, there has been a significant effort underway to develop materials and ceramic honeycomb articles which exhibit high thermal shock resistance and combinations of porosity, Coefficient of Thermal Expansion (CTE), and Modulus Of Rupture (MOR) suitable for these more severe diesel particulate filter applications. In particular, aluminum titanate ceramics have emerged as an excellent candidate for such high-temperature applications. In order to achieve the desired high porosity in such aluminum titantate materials, generally above 40%, graphite pore formers have been added to the inorganic batch materials. However, the addition of graphite undesirably may result in very long firing cycles (for example, in excess of 180 hours) to achieve burnout of the graphite without causing part cracking. Furthermore, high levels of graphite are not desired because of the adverse effect on dielectric drying, a conventional approach for drying green bodies formed of inorganic materials.
Thus, it should be recognized that there is an unmet need for a way of achieving the desired high porosity in aluminum titanate articles while doing so with reduced firing cycle length and/or without producing cracked parts and/or complicating the drying process.